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The Dawn spacecraft, after more than seven years in space, has entered the final phase of its trek to Ceres.

NASA said Wednesday that Dawn is now about 640,000 kilometers from the dwarf planet and is expected to arrive in orbit on March 6.

Ceres is the largest object in the asteroid belt, with an average diameter of about 950 kilometers.

Dawn’s visit to Ceres will make it the first spacecraft ever to orbit two different celestial objects. The probe also orbited the protoplanet Vesta in 2011-2012.

Although discovered more than 200 years ago, scientists know little about Ceres. The closest dwarf planet to Earth, it may have both an ocean and an atmosphere. Ceres is so cold that water would sublimate if it wre on the surface.

It is difficult to choose the most fantastic space-related photograph of the year. There are, after all, many contenders. We had, for example, many “first-time” pictures of features on the Red Planet, our neighbor Mars. This one shows the west rim of huge Endeavor crater, which has a diameter of about 14 miles. The crater is characterized by geological features that are older than any others Opportunity has investigated during its mission.

Photo courtesy NASA/JPL-Caltech/Cornell/ASU

Then there was the first image ever obtained of the huge asteroid known as Vesta. NASA’s Dawn mission is in the midst of an exploration of the asteroid belt. This full view of Vesta was taken from a distance of 5,200 kilometers. The asteroid has a mean diameter of about 530 kilometers and is the second-largest object in the asteroid belt, second in size only to the dwarf planet Ceres.

Photo courtesy NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Sticking with the space theme, there are many other amazing images to see, starting with this dramatic one from the MESSENGER probe that shows just a small part of Mercury:

We cannot forget the incredible images obtained by the Hubble Space Telescope, either. This one, obtained by the telescope in Feb. 2011, shows a nebula (a region of space in which stars are being formed) that is about 2,000 light years away from Earth:

Photo courtesy NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

But my favorite picture from 2011 is this one, which was obtained by NASA’s Cassini probe. It shows a storm encircling the huge planet. The storm is the most intense, and the largest, ever observed by Cassini. It produces a significant amount of radio noise, which indicates that there is lightning occurring in Saturn’s atmosphere. One odd feature of storms on Saturn is that they occur when a huge amount of energy is released all at once, which is unlike the meteorological pattern on other planets.